simobserve

simobserve(project='sim', skymodel='', inbright='', indirection='', incell='', incenter='', inwidth='', complist='', compwidth='"8GHz"', comp_nchan=1, setpointings=True, ptgfile='$project.ptg.txt', integration='10s', direction='', mapsize=['', ''], maptype='hexagonal', pointingspacing='', caldirection='', calflux='1Jy', obsmode='int', refdate='2014/01/01', hourangle='transit', totaltime='7200s', antennalist='', sdantlist='aca.tp.cfg', sdant=0, outframe='LSRK', thermalnoise='tsys-atm', user_pwv=0.5, t_ground=270.0, t_sky=260.0, tau0=0.1, seed=11111, leakage=0.0, graphics='both', verbose=False, overwrite=True)[source]

visibility simulation task

[Description] [Examples] [Development] [Details]

Parameters

  • project (string=’sim’) - Root prefix for output file names

  • skymodel (string=’’) - model image to observe

    skymodel != ''

    • inbright (string=’’) - Peak brightness to scale the image to in Jy/pixel

    • indirection (string=’’) - Set new direction, e.g. J2000 19h00m00 -40d00m00

    • incell (string=’’) - Set new cell/pixel size, e.g. 0.1arcsec

    • incenter (string=’’) - Set new frequency of center channel e.g. 89GHz (required even for 2D model)

    • inwidth (string=’’) - Set new channel width, e.g. “10MHz” (required even for 2D model)

  • complist (string=’’) - Componentlist to observe

    complist != ''

    • compwidth (string=‘“8GHz”’) - Bandwidth of components

    • comp_nchan (int=1) - Channelization of components

  • setpointings (bool=True) - Calculate a map of pointings?

    setpointings = True

    • integration (string=’10s’) - Integration (sampling) time

    • direction (stringVec=’’) - Mosaic center direction, e.g J2000 19h00m00 -40d00m00

    • mapsize (stringVec=[‘’, ‘’]) - Angular size of mosaic map to simulate.

    • maptype (string=’hexagonal’) - how to calculate the pointings for the mosaic observation: hexagonal, square (raster), ALMA, etc.

    • pointingspacing (string=’’) - Spacing in between pointings e.g. 0.25PB. ALMA default: INT=lambda/D/sqrt(3), SD=lambda/D/3

    setpointings = False

    • ptgfile (string=’$project.ptg.txt’) - List of pointing positions

    • integration (string=’10s’) - Integration (sampling) time

  • obsmode (string=’int’) - Observation mode to simulate [int(interferometer)|sd(singledish)|(none)]

    obsmode = int

    • antennalist (string=’’) - Interferometer antenna position file

    • refdate (string=’2014/01/01’) - Date of observation. Not critical unless concatting simulations

    • hourangle (string=’transit’) - Hour angle of observation center, e.g. -3:00:00, 5h

    • totaltime (string=’7200s’) - Total time of observation or number of repetitions

    • caldirection (string=’’) - pt source calibrator [experimental]

    • calflux (string=’1Jy’) - pt source calibrator flux [experimental]

    obsmode = sd

    • sdantlist (string=’aca.tp.cfg’) - Single dish antenna position file

    • sdant (int=0) - Single dish antenna index in file

    • refdate (string=’2014/01/01’) - Date of observation. Not critical unless concatting simulations

    • hourangle (string=’transit’) - Hour angle of observation center, e.g. -3:00:00, 5h

    • totaltime (string=’7200s’) - Total time of observation or number of repetitions

    obsmode = ''

    • antennalist (string=’’) - Interferometer antenna position file

    • sdantlist (string=’aca.tp.cfg’) - Single dish antenna position file

    • sdant (int=0) - Single dish antenna index in file

  • outframe (string=’LSRK’) - Spectral frame of MS to create

  • thermalnoise (string=’tsys-atm’) - add thermal noise: [tsys-atm|tsys-manual|(none)]

    thermalnoise = tsys-atm

    • user_pwv (double=0.5) - Precipitable Water Vapor in mm

    • t_ground (double=270.) - Ground/spillover ambient temperature in K

    • seed (int=11111) - Random number seed

    thermalnoise = tsys-manual

    • t_ground (double=270.) - Ground/spillover ambient temperature in K

    • t_sky (double=260.) - Atmospheric temperatur in K

    • tau0 (double=0.1) - Zenith opacity

    • seed (int=11111) - Random number seed

  • leakage (double=0.0) - Cross polarization (interferometer only)

  • graphics (string=’both’) - Display graphics at each stage to [screen|file|both|none]

  • verbose (bool=False) - Print extra information to the logger and terminal

  • overwrite (bool=True) - Overwrite existing files in the project subdirectory

Description

Warning

There are Known Issues for simobserve.

This task simulates interferometric or total power MeasurementSets. The general steps for simulation in CASA are described on the top Simulation page. We describe the first two steps in more detail here.

  1. Make a model image or componentlist representation of the sky brightness distribution.

  2. Use the simobserve task to create a MeasurementSet (uv data).

Generating a Model Image

A “model image” is a CASA image or FITS file that contains a representation of the sky brightness distribution, and it represents the object to be “observed” in the simulation. There are several ways to generate a model image.

Starting from an existing FITS image

The simplest option is to begin with an existing FITS image. The image can be either a single plane (i.e., one observed frequency channel) or a cube. A common simulation exercise is to begin with a FITS file representing an observation of a target, then scale the spatial axes and the flux to shift the data to what would be observed for a similar target at a different distance. The simobserve task has parameters to set the peak flux density, coordinates on the sky, pixel size, frequency of the center channel, and channel width.

Starting from a component list

Warning

WARNING: simobserve does not currently handle component lists correctly for single-dish-only simulations. It is advised to convert the component list to an image or FITS file.

It may be useful to simulate observations of an idealized model image consisting, for example, of point sources and Gaussians. The CASA component list tool (cl) allows the user to specify a set of point sources, Gaussians, and disks. One can then either use that component list directly in simobserve, or create a CASA image from the components, or both. Details can be found in the Simulations CASA guide entitled ‘Simulation Guide Component Lists’.

Starting from a GIF or JPG image

A user may wish to convert a GIF or JPG image to a FITS file for simulation in CASA. The image should be converted to a 32-bit FITS image for use with the CASA sim tools. Alternatively, you could use ImageMagik from the command line, like so:

convert myfile.jpg myfile.fits

Then proceed to trim and convert the file in CASA like so:

importfits(fitsimage='myfile.fits',imagename='testimage',overwrite=T)

default 'immath'
imagename = 'testimage'
expr = 'IM0'
box = '0,0,299,299'
outfile = 'testimage2'
immath()

You can use imhead to modify the header parameters of the new image, or you can use the parameters in the simobserve task to modify the peak flux density, coordinates on the sky, pixel size, frequency of the center channel, and channel width. See the discussion below.

Generating visibilities with simobserve

The task simobserve takes several steps to generate observed visibilities. The major steps are:

  • Modify Model: If desired, you can modify the header parameters in your data model to mimic different observing targets. For example, if you start with a model of M100 you might wish to scale the axes to simulate an observation of an M100-like galaxy that is 4X more distant.

  • Set Pointings: If the angular size of your model image is comparable or larger than the 12-m primary beam, you can simulate observing the target as a mosaic. In this step, the individual pointings are determined and saved in a text file. You can also generate such a text file yourself.

  • Generate visibilities: The visibilities are determined based on the telescope and configuration specified, and the length in time of the observation.

  • Finally, noise can be added to the visibilities. The simobserve task uses the aatm atmospheric model (based on Juan Pardo’s ATM library) to simulate real observing conditions. It can corrupt the data with thermal noise and atmospheric attenuation. Corruption with an atmospheric phase screen, or adding gain fluctuations or drift, can be added subsequently using the simulator tool sm as described in the Simulations CASA Guide entitled ‘Corrupting Simulated Data (Simulator Tool)’.

For details, please see the descriptions of the individual parameters below.

Warning

WARNING: It is currently not possible to generate a MS in a frame other than J2000 e.g., if you set indirection to “ICRS 19h00m00 -40d00m00” it will silently assume that to actually be “J2000 19h00m00 -40d00m00”. The reference frame can be set to ICRS during the imaging or simanalyze process.

Warning

WARNING: when using a simulated MS in tclean, it should be considered best practice to declare the phasecenter parameter using the ‘J2000 xx:xx:xx.xxx +xxx.xx.xx.xxx’ notation to account for possible rounding errors that can create an offset in the simulated image.

Note

NOTE: simobserve calls sm.predict with sm.setvp (dovp=True). This means that the vpmanager will be queried, and a primary beam pattern will be applied, according to the telescope name. One can set the primary beam for the given telescope using the vpmanager. In most circumstances, simobserve will use synthesis gridding (image-plane primary beam application), unless 1) there are more than 1 pointing, AND 2) there are more than one antenna diameter in the configuration file. In that case it will sm.setoptions (ftmachine=”mosaic”) which enables heterogenous array simulation for ALMA, ACA, and OVRO telescopes.

Treatment of the primary beam depends critically on parameters set in sm.setvp() and sm.setoptions(ftmachine) - see help sm.setvp for details. For componentlists, if sm.setvp() is run prior to predict, then the spectral variation of each component in the componentlist will include the multiplicative term of the beam value for each channel frequency. So a flat spectrum component will show the frequency variation of the beam in the predicted visibilities.

Task output

Below is a list of the products produced by the simobserve task. Not all of these will necessarily be produced, depending on input parameters selected.

Note

NOTE: To support different runs with different arrays, the names have the configuration name from antenna list appended.

  • [project].[cfg].skymodel = 4D input sky model image (optionally) scaled

  • [project].[cfg].skymodel.flat.regrid.conv = input sky regridded to match the output image, and convolved with the output clean beam

  • [project].[cfg].skymodel.png = diagnostic figure of sky model with pointings

  • [project].[cfg].ptg.txt = list of mosaic pointings

  • [project].[cfg].quick.psf = psf calculated from uv coverage

  • [project].[cfg].ms = noise-free MeasurementSet

  • [project].[cfg].noisy.ms = corrupted MeasurementSet

  • [project].[cfg].observe.png = diagnostic figure of uv coverage and visibilities

  • [project].[cfg].simobserve.last = saved input parameters for simobserve task

Parameter descriptions

project

The root filename for all output files. This parameter should be set to the same name as used when running simanalyze or simalma for the directory of results generated.

skymodel

The input image (used as a model of the sky). simobserve uses a CASA or FITS image. If you merely have a grid of numbers, you will need to write them out as FITS or write a CASA script to read them in and use the ia tool to create an image and insert the data. simobserve does NOT require a coordinate system in the header. If the coordinate information is incomplete, missing, or you would like to override it, set the appropriate “in” parameters.

Note

NOTE: Setting those parameters simply changes the header values, ignoring any values already in the image. No regridding is performed.

You can also manipulate an image header manually with the imhead task. If you have a proper Coordinate System, simobserve will do its best to generate visibilities from that.

skymodel expandable parameters

inbright

Scales the model flux densities by setting the peak brightness of the britest pixel in Jy/pixel, or ‘’ for unchanged.

Warning

WARNING: ‘unchanged’ will take the numerical values in your image and assume they are in Jy/pixel, even if it says some other unit in the header.

indirection

The central direction to place the sky model image, or ‘’ to use whatever is in the image already.

incell

The spatial pixel size to scale the skymodel image, or ‘’ to use whatever is in the image already.

incenter

The frequency to use for the center channel (or only channel, if the skymodel is 2D). Examples: incenter=’89GHz’, or ‘’ to use what is in the header. This will also become the default rest frequency, e.g. when imaging with tclean.

inwidth

The width of the channels to use, or ‘’ to use what is in the image should be a string representing a quantity with units. Examples: inwidth=’10MHz’

Note

NOTE: inwidth only works reliably with frequencies, not velocities.

Note

NOTE 2: It is not possible to change the number of spectral planes of the sky model, only to relabel them with different frequencies. That kind of regridding can be accomplished with the CASA toolkit.

complist

A component list model of the sky, added to or instead of skymodel.

Warning

WARNING: simobserve does not currently handle component lists correctly for single-dish-only simulations. It is advised to convert the component list to an image or FITS file.

complist expandable parameters

compwidth

The bandwidth of components; if simulating from components only, this defines the bandwidth of the MS and output images.

comp_nchan

The number of channels in the output MS. Validated only for a positive integer number of channels, this parameter assumes a flat spectrum and equal spacing when setting the channel width in the output MS. Since variation in channel width as a function of frequency is not currently supported, it is not advised to use this parameter to simulate observations with spectral index or large fractional bandwidth (use a skymodel image instead).

setpointings

If True, simobserve calculates a map of pointings based on a set of sub-parameters and generates a pointing file. If False, it will read the pointings from the parameter ptgfile.

setpointings=True expandable parameters

integration

Sets the time interval for each integration. Also used with setpointings=False. Examples: integration=’10s’

Note

NOTE: To simulate a ‘scan’ longer than one integration, use setpointings to generate a pointing file, and then edit the file to increase the time at each point to be larger than the parameter integration time.

direction

The mosaic center direction. If left unset, simobserve will use the center of the skymodel image. Examples: direction= ‘J2000 19h00m00 -40d00m00’; can optionally be a list of pointings, otherwise simobserve will cover a region of size mapsize according to maptype.

mapsize

The angular size of mosaic map to simulate. Set to ‘’ to cover the model image.

maptype

How to calculate the pointings for the mosaic observation. ‘hexagonal’, ‘square’ (rectangular raster), ‘ALMA’ for the same hex algorithm as the ALMA Cycle 1 OT or ‘ALMA2012’ for the algorithm used in the Cycle 0 OT.

pointingspacing

Spacing in between primary beams. “0.25PB” to use 1/4 of the primary beam FWHM, “nyquist” will use \(\lambda/d/2\), ‘’ will use \(\lambda/d/\sqrt(3)\) for INT, \(\lambda/d/3\) for SD.

setpointings=False expandable parameters

ptgfile

A text file specifying directions in the following format, with optional integration times, e.g.,

#Epoch     RA          DEC      TIME(optional)
J2000 23h59m28.10 -019d52m12.35 10.0

If the time column is not present in the file, it will use ‘integration’ for all pointings.

Note

NOTE: At this time the file should contain only science pointings: simobserve will observe these, then optionally the calibrator, then the list of science pointings again, etc, until totaltime is used up.

obsmode

Sets the observation mode to calculate visibilities from a skymodel image (which may have been modified above), an optional component list, and a pointing file (which also may have been generated above). This parameter takes two possible values:

  • interferometer (or int)

  • singledish (or sd)

If simulating from a component list, you should specify compwidth, the desired bandwidth. There is not currently a way to specify the spectrum of a component, so simulations from a componentlist only will be continuum (1 chan).

obsmode expandable parameters (‘int’ or ‘sd’)

refdate

The date of simulated observation. Examples: refdate=’2014/05/21’

hourangle

The hour angle of observation, given as a string of various possible formats. E.g., “-3:00:00”, or “5h”. The default setting for this parameter is hourangle=’transit’, which is equivalent to 0h.

totaltime

The total time of an observation. Examples: totaltime=’7200s’ or if a number without units, interpreted as the number of times to repeat the mosaic.

obsmode=’int’ expandable parameters

antennalist

ASCII file containing antenna positions. Each row has x, y, and z coordinates and antenna diameter and name; header lines are required to specify the observatory name and coordinate system. If the configuration file does not include antenna names, the station name will be used instead.

#observatory=ALMA
#COFA=-67.75,-23.02
#coordsys=LOC (local tangent plane)
# uid___A002_Xdb6217_X55ec_target.ms
# x             y               z             diam  station  ant 
-5.850273514   -125.9985379    -1.590364043   12.   A058     DA41
-19.90369337    52.82680653    -1.892119601   12.   A023     DA42
13.45860758    -5.790196849    -2.087805181   12.   A035     DA43
5.606192499     7.646657746    -2.087775605   12.   A001     DA44
24.10057423    -25.95933768    -2.08466565    12.   A036     DA45

Standard array configuration files are found in your CASA data repository, os.getenv(“CASAPATH”).split()[0]+”/data/alma/simmos/”. A string of the form “alma;0.5arcsec” will be parsed into a full 12m ALMA configuration. If antennalist=’ ‘, simobserve will not produce an interferometric MS. If simulating total power observations, be sure to accurately set the parameter sdantlist.

caldirection

An unresolved calibrator can be observed interleaved with the science pointings. The calibrator is implemented as a point source clean component with this specified direction and flux= calflux.

calflux

Sets the flux density for the calibrator. Default is set to calflux=’1Jy’.

obsmode=’sd’ expandable parameters

sdantlist

Single-dish antenna position file. If simulating total power observations, be sure to accurately set the parameter sdantlist. If this parameter is left unset, simobserve assumes the default configuration file for a single dish simulation (even if the configuration file is explicitly specified in antennalist). Default: sdantlist=’aca.tp.cfg’.

sdant

The index of the antenna in the list to use for total power. Defaults to the first antenna on the list (sdant=0). Heterogeneous total power “arrays” are not currently supported.

thermalnoise

Adds thermal noise to the synthesized data. This parameter takes two possible values (not including unset ‘ ‘):

  • tsys-atm: J. Pardo’s ATM library will be used to construct an atmospheric profile for the ALMA site: altitude 5000m, ground pressure 650mbar, relhum=20%, a water layer of user_pwv at altitude of 2km, the sky brightness temperature returned by ATM, and internally tabulated receiver temperatures

  • tsys-manual: instead of using the ATM model, specify the zenith sky brightness and opacity manually. Noise is added and then the visibility flux scale is referenced above the atmosphere.

In either mode, noise is calculated using the following assumptions:

  • an antenna spillover efficiency of 0.96,

  • taper of 0.86,

  • surface accuracy of 25 and 300 microns for ALMA and EVLA, respectively, using the Ruze formula for surface efficiency,

  • correlator efficiencies of 0.95 and 0.91 for ALMA and EVLA, and

  • receiver temperatures:

    • for ALMA: 25, 30, 40, 42, 50, 50, 72, 135, 105, 230 K interpolated between 35, 75, 110, 145, 185, 230, 345, 409, 675, 867 GHz

    • for EVLA: 500, 70, 60, 55, 100, 130, 350 K interpolated between 0.33, 1.47, 4.89, 8.44, 22.5, 33.5, 43.3 GHz

    • for SMA: 67, 116, 134, 500 K interpolated between 212, 310, 383, 660 GHz

These are only approximate numbers and do not take into account performance at edges of receiver bands, nor are they guaranteed to reflect the most recent measurements. Caveat emptor. Use the sm tool to add noise if you want more precise control, and use the ALMA exposure time calculator for sensitivity numbers in proposals.

thermalnoise expandable parameters

t_ground

The ambient ground/spillover temperature in K.

seed

Random number seed for noise generation.

thermalnoise=’tsys-atm’ expandable parameters

user_pwv

The precipitable water vapor at zenith if constructing an atmospheric model.

thermalnoise=’tsys-manual’ expandable parameters

t_sky

The atmospheric temperature in K.

tau0

The zenith opacity at observing frequency. See here for more information on noise, in particular how to add a phase screen using the toolkit.

leakage

Adds cross polarization corruption of this fractional magnitude.

graphics

View plots on the screen, saved to file, both, or neither.

verbose

Turns on or off the printing of extra information to the logger and terminal.

overwrite

Overwrites existing files in the project subdirectory. Default: False

Examples

This example was taken from the Simulations CASA Guide entitled ‘Simulations Guide Component List’.

default("simobserve")
project = "FITS_list"
skymodel = "Gaussian.fits"
inwidth = "1GHz"
complist = 'point.cl'
compwidth = '1GHz'
direction = "J2000 10h00m00.0s -30d00m00.0s"
obsmode = "int"
antennalist = 'alma.cycle9.1.cfg'
totaltime = "28800s"
mapsize = "10arcsec"
thermalnoise = ''
simobserve()

This example demonstrates the use of the comp_nchan parameter to simulate a disk and produce a multi-channel MS (with a flat spectrum).

simobserve(project="test_project",
           complist="complist.cl",
           compwidth="2000.00MHz",
           comp_nchan=128,
           integration="6.05s",
           mapsize=['11.51arcsec'],
           hourangle="1.5h",
           totaltime="677.6s",
           antennalist="antennalist.cfg",
           sdantlist="aca.tp.cfg",
           thermalnoise="")

This example shows how to assign a central rest-frequency and channel width to a simulated image cube.

simobserve(project=‘model_cube’, 
           skymodel=‘skymodel.image', 
           inwidth='0.4MHz', 
           antennalist='alma.cycle6.1.cfg', 
           direction="J2000 16h59m41.63s -40d03m43.61s", 
           obsmode="int", mapsize="2arcmin", 
           totaltime="1800s", 
           thermalnoise='', 
           incenter='86.6425GHz')

This produces a data cube with a central rest-frequency of 86.6425 GHz and a channel width of 0.4 MHz. Note the Known Issue for simobserve that inwidth should not be specified in km/s.

Development

No additional development details

Parameter Details

Detailed descriptions of each function parameter

project (string='sim') - root prefix for output file names
skymodel (string='') - Model image to observe
* simobserve uses a CASA or fits image. If you
merely have a grid of numbers, you will need to
write them out as fits or write a CASA script to
read them in and use the ia tool to create an
image and insert the data.
* simobserve does NOT require a coordinate system
in the header. If the coordinate information is
incomplete, missing, or you would like to
override it, set the appropriate “in”
parameters. NOTE that setting those parameters
simply changes the header values, ignoring any
values already in the image. No regridding is
performed.
* You can also manipulate an image header manually
with the “imhead” task.
* If you have a proper Coordinate System,
simobserve will do its best to generate
visibilities from that.
inbright (string='') - Peak brightness to scale the image to, in Jy/pixel
Subparameter of skymodel
Default: ‘’ (i.e., unchanged)
Example: inbright=’1.2Jy/pixel’
Note: “unchanged” will take the numerical values
in your image and assume they are in Jy/pixel,
even if it says some other unit in the header.
indirection (string='') - Central direction to place the sky model image
Subparameter of skymodel
Default: ‘’ (use whatever is in the image
already)
Example: indirection=’J2000 19h00m00
-40d00m00’
incell (string='') - set new cell/pixel size
Subparameter of skymodel
Default: ‘’ (use whatever is in the image
already)
Example: incell=’0.1arcsec’
incenter (string='') - Frequency to use for the center channel (or only channel,
if the skymodel is 2D).
Subparameter of skymodel
Default: ‘’ (use whatever is in the image
already)
This will also become the default rest frequency, e.g. when imaging with tclean.
Example: incenter=’89GHz’
inwidth (string='') - Set new channel width
Subparameter of skymodel
Default: ‘’ (use whatever is in the image
already)

Should be a string representing a quantity with
units e.g. inwidth=’10MHz’
NOTES:
* Only works reliably with frequencies, not
velocities
* It is not possible to change the number of
spectral planes of the sky model, only to relabel
them with different frequencies That kind of
regridding can be accomplished with the CASA
toolkit.
complist (string='') - Component list model of the sky, added to or instead of skymodel.
compwidth (string='"8GHz"') - Bandwidth of components
Subparameter of complist
If simulating from components only, this defines
the bandwidth of the MS and output images
Example: compwidth=’8GHz’
comp_nchan (int=1) - Channelization of components
Subparameter of complist
If simulating from components only, this defines
the number of channels of the MeasurementSet
Example: comp_nchan=256
setpointings (bool=True) - If true, calculate a map of pointings and write ptgfile. If false, read pointings from ptgfile.
Default: True
If graphics are on, display the pointings shown
on the model image
ptgfile (string='$project.ptg.txt') - A text file specifying directions
Subparameter of setpointings=False

The text file should have the following format,
with optional integration times:
Epoch RA DEC TIME(optional)
J2000 23h59m28.10 -019d52m12.35 10.0
If the time column is not present in the file, it
will use “integration” for all pointings.
NOTE: at this time the file should contain only
science pointings: simobserve will observe these,
then optionally the calibrator, then the list of
science pointings again, etc, until totaltime is
used up.
integration (string='10s') - Time interval for each integration
Subparameter of setpointings=False
Example: integration=’10s’
NOTE: to simulate a “scan” longer than one
integration, use setpointings to generate a
pointing file, and then edit the file to increase
the time at each point to be larger than the
parameter integration time.
direction (stringVec='') - Mosaic center direction.
Subparameter of setpointings=True
Example: “J2000 19h00m00 -40d00m00” or “” to
center on model
If unset, will use the center of the skymodel
image.
* can optionally be a list of pointings, otherwise
* simobserve will cover a region of size mapsize
according to maptype
mapsize (stringVec=['', '']) - Angular size of of mosaic map to simulate.
Subparameter of setpointings=True
Set to “” to cover model
maptype (string='hexagonal') - How to calculate the pointings for the mosaic
observation?
Subparameter of setpointings=True
Options: hexagonal, square (raster), ALMA, etc
“ALMA” for the same hex algorithm as the ALMA
Cycle 1 OT or “ALMA2012” for the algorithm used
in the Cycle 0 OT
pointingspacing (string='') - Spacing in between pointings.
Subparameter of setpointings=True
Examples:
pointingspacing=”0.25PB”
pointingspacing=”” for ALMA default
INT=lambda/D/sqrt(3), SD=lambda/D/3
caldirection (string='') - pt source calibrator [experimental]
calflux (string='1Jy') - pt source calibrator flux [experimental]
obsmode (string='int') - Observation mode to simulate
Options: int(interferometer)|sd(singledish)|””(none)
Observation mode to calculate visibilities from a
skymodel image (which may have been modified
above), an optional component list, and a
pointing file (which also may have been generated
above).
This parameter takes two possible values:
- interferometer (or int)
- singledish (or sd)
* If graphics are on, this observe step will
display the array (similar to plotants), the uv
coverage, the synthesized (dirty) beam, and
ephemeris information
* If simulating from a component list, you should
specify “compwidth”, the desired bandwidth; and
specify “comp_nchan”, the desired channelization
if more than one output channel is desired
refdate (string='2014/01/01') - Date of simulated observation
Subparameter of obsmode=’int|sd’
Not critical unless concatting simulations
Example: refdate=”2014/05/21”
hourangle (string='transit') - Hour angle of observation center.
Subparameter of obsmode=’int|sd’
Examples:
hourangle=”-3:00:00”, “5h”, or “transit”
totaltime (string='7200s') - Total time of observation or number of repetitions
Subparameter of obsmode=’int|sd’
Example:
totaltime=’7200s’
If a number without units, interpreted as the
number of times to repeat the mosaic.
antennalist (string='') - Text file containing antenna positions.
Subparameter of obsmode=’int|””’
Each row has x y z coordinates and antenna diameter
with optional station name and antenna name.
Header lines are required to specify:
# observatory=ALMA
# coordsys=UTM
If the Universal Transverse Mercator projection is
specified, then other keywords are required:
# datum=WGS84
# zone=19
# hemisphere=S
If the observatory keyword is not defined, then the
COFA keyword should be, using a coordinate pair:
#COFA=-67.75,-23.02
* Standard array configurations are found in your
CASA data repository,
* If “”, simobserve will not not produce an
interferometric MS
* A string of the form “alma;0.5arcsec” will be
parsed into a full 12m ALMA configuration.
sdantlist (string='aca.tp.cfg') - single dish antenna position file
Subparameter of obsmode=’sd|””’
sdant (int=0) - Index of the antenna in the list to use for total power.
Subparameter of obsmode=’sd|””’
Default: first antenna on the list.
outframe (string='LSRK') - spectral frame of MS to create
Subparameter of obsmode=’sd|””’
thermalnoise (string='tsys-atm') - add thermal noise.
Options: tsys-atm, tsys-manual, “”
This parameter accepts two settings:
- tsys-atm: J. Pardo’s ATM library will be used
to construct an atmospheric profile for the ALMA
site: altitude 5000m, ground pressure 650mbar,
relhum=20%, a water layer of user_pwv at altitude
of 2km, the sky brightness temperature returned
by ATM, and internally tabulated receiver
temperatures.
- tsys-manual: instead of using the ATM model,
specify the zenith sky brightness and opacity
manually. Noise is added and then the visibility
flux scale is referenced above the atmosphere.
If left unset (empty string) no thermalnoise
corruption is performed.

In either mode, noise is calculated using an
antenna spillover efficiency of 0.96, taper of
0.86, surface accuracy of 25 and 300 microns for
ALMA and EVLA respectively (using the Ruze
formula for surface efficiency), correlator
efficiencies of 0.95 and 0.91 for ALMA and EVLA,
receiver temperatures
for ALMA of 17, 30, 37, 51, 65,
83,147,196,175,230 K interpolated between 35,
75,110,145,185,230,345,409,675,867 GHz,
for EVLA of 500, 70, 60, 55, 100, 130, 350 K
interpolated between
0.33,1.47,4.89,8.44,22.5,33.5,43.3 GHz,
for SMA of 67, 116, 134, 500 K interpolated
between 212.,310.,383.,660. GHz.
Note: These are only approximate numbers and do
not take into account performance at edges of
receiver bands, neither are they guaranteed to
reflect the most recent measurements. Caveat
emptor. Use the sm tool to add noise if you want
more precise control, and use the ALMA exposure
time calculator for sensitivity numbers in
proposals.
user_pwv (double=0.5) - Precipitable water vapor if constructing an atmospheric
model (in mm)
Subparameter of thermalnoise=’tsys-atm’
t_ground (double=270.) - Ground/spillover temperature in K
Subparameter of
thermalnoise=’tsys-atm|tsys-manual’
t_sky (double=260.) - Atmospheric temperature in K
Subparameter of thermalnoise=’tsys-manual’
tau0 (double=0.1) - Zenith opacity at observing frequency
Subparameter of thermalnoise=’tsys-manual’
See the Simulations CASA Guide (https://casaguides.nrao.edu) on ‘Corrupting Simulated Data’ for more information on noise, in particular how to add a phase screen using the toolkit
seed (int=11111) - Random number seed
Subparameter of
thermalnoise=’tsys-atm|tsys-manual’
leakage (double=0.0) - add cross polarization corruption of this fractional
magnitude (interferometer only)
graphics (string='both') - View plots on the screen, saved to file, both, or neither
Options: screen|file|both|none
verbose (bool=False) - Print extra information to the logger and terminal
Default: False
Options: True|False
overwrite (bool=True) - Overwrite files starting with $project
Default: False
Options: True|False